This has been confirmed by the gravitational event GW170817 ([1]}, due to MNS, where r-process elements have been detected ([2]}, [3]}, [4]}, [5]}). The Eu is easily observable in stellar atmospheres and is a pure r-process element, therefore most chemical evolution models refer to this element. [6]} included nucleosynthesis from merging of compact objects in the two-infall model and followed in detail the evolution of the abundances of Eu and Fe in the Milky Way. Concerning Eu, both CC-SNe and MNS were taken into account as Eu producers. The main conclusions in that paper can be summarized as follows: i) if each merging event produces \(\sim 3\cdot 10^{-6}\,M_{\odot }\)  of Eu and the time delay for merging, due to gravitational-wave emission, is constant and short (\(\sim \)  1 Myr) for all systems, and the progenitors of neutron stars (or black holes) giving rise to the merging lie in the range 9–50 \(M_{\odot }\) , then MNS can be responsible of the entire Eu production in the solar vicinity; ii) If, instead, the time delays for merging are longer, then also CC-SNe need to be considered as Eu producers to fit the observed [Eu/Fe] vs. [Fe/H] plot at low metallicities. In this case, the amount of Eu produced per merging event should be lower (\(\sim 2\cdot 10^{-6}\,M_{\odot }\) ), but always in the range suggested by nucleosynthesis calculations (\(10^{-7}\) –\(10^{-5}\,M_{\odot }\) , [7]}) and at the lower extreme of the range suggested for GW170817. This conclusion was confirmed by other papers ([8]}, [9]}; [10]}, [11]}. In Fig. REF  we show the results of [6]} for [Eu/Fe] vs. [Fe/H] in the cases of only MNS as Eu producers and of both CC-SNe and MNS.
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